1. Field of the Invention
The present invention relates to a dynamoelectric machine such as an automotive alternator, etc., and particularly relates to a Lundell rotor construction to which permanent magnets are mounted.
2. Description of the Related Art
Automotive alternators that use Lundell rotors have been used in automobiles for decades. Loads from electrical equipment that has been mounted due to environmental issues have increased rapidly in recent years, and further increases in generated power have been sought from Lundell rotors.
Conventionally, means of disposing permanent magnets between claw-shaped magnetic poles that face each other circumferentially in a Lundell rotor have been adopted in order to solve such problems (see Patent Literature 1 and 2, for example).
A means has also been adopted of holding permanent magnets inside pockets that are formed integrally on fans, mounting a fan onto a first pole piece by press-fitting the pockets between an upper surface of a body of the first pole piece and lower surfaces of pole fingers of a second pole piece, and mounting a fan to the second pole piece by press-fitting the pockets between an upper surface of a body of the second pole piece and lower surfaces of pole fingers of the first pole piece (see Patent Literature 3, for example).
Patent Literature 1: Japanese Patent Laid-Open No. SHO 61-85045 (Gazette)
Patent Literature 2: U.S. Pat. No. 4,959,577 (Specification)
Patent Literature 3: Japanese Patent Publication No. 2002-527015 (Gazette)
In Patent Literature 1 and 2, when holding the permanent magnets between the claw-shaped magnetic pole portions, it is necessary to position the permanent magnets relative to the facing claw-shaped magnetic pole portions with high precision, making it necessary to add a magnet holding member, or to form magnet holding grooves on the claw-shaped magnetic pole portions by machining, leading to steep rises in production costs and reductions in mass producibility.
In the technique according to Patent Literature 3, the pockets that hold the permanent magnets are formed so as to have an approximately rectangular cross-sectional shape that conforms to an interfitting space between the body of one pole piece and the pole fingers of the other pole piece. In order to strengthen the hold on the pockets that hold the permanent magnets, it is necessary to machine the interfitting surfaces of the pole pieces with high precision. However, the surfaces of the pole pieces that fit together with the pockets are flat surfaces or gently curved surfaces, and after-processing of the pole pieces by high-performance machine tools is required, requiring huge machining costs and machining time. Because displacement of tip ends of the claw-shaped magnetic pole portions in excess of 100 μm radially outward also arises during high-speed rotation, stable holding of the permanent magnets cannot be achieved in a construction in which centrifugal forces that act on the pockets that hold the permanent magnets are held by tip end inner circumferential surfaces of the claw-shaped magnetic pole portions. Because the permanent magnets are insert-molded into the fans, the permanent magnets may be displaced radially outward together with the displacement of the tip ends of the claw-shaped magnetic pole portions during high-speed rotation, and there has been a risk that excessive stresses may act on the fans and damage the fans.